Abrasive article



Jan. 26, 1943.

E. PQDAHLSTROM ET AL ABRASIVE ARTICLE Filed March 10, 1941 INVENTORS.ERIC. PJDAHLS'TROM EDGAR HORNE ATTORNEY Patented Jan. 26, 1943 amusrvnARTIC E Eric P. Dahlstrom, Niagara. Falls, N. Y., and Edgar Horne,Niagara Falls, Ontario, Canada, assignors to The Carborundum Company,Niagara Falls, N. Y., a corporation of Delaware.

Application March 10, 1941, Serial No. 382,520

6 Claims. (Cl. 51-188) This invention relates to endless abrasive beltsformed from strips of flexible, abrasive coated,

web material. More particularly the invention is concerned with methodsof joining the ends of the abrasive strips together and to the productresulting from such methods.

Heretofore abrasive belts have been formed by splicing, i. e., byoverlapping and joining, the ends of a strip of coated abrasive with asuitable adhesive between the laps. Usually the abrasive coating isremoved from one end of the strip by grinding-an operation referred toin the art as skiving--- and the opposite end of the strip placed uponand adhered. to the skived area. Such splices are thicker than theabrasive strip and as a result undesirable effects are brought out bythisthicker portion as the belt is used. For example, there is apounding action which separates the work momentarily from the abr'adingsurface at each revolution of the belt and reduces the contact time andcutting efficiency; furthermore, the pounding of the thicker spliceportion is objectionable as it causes difliculty in generating flatsurfaces at the boundaries of the work piece, and the excessivethickness encourages premature belt breakage at the splice.

Belts of uniform thickness have been made by butt-joining the ends of anabrasive strip and at the same time adhering this strip to an inner,non-abrasive strip or liner, but this construction the use of a fulllength of liner material plus the quantity of adhesive necessary to jointhe liner and the abrasive strip. 7

a is more expensive than a plain belt as it involves I It is thereforeincluded in the objects of this invention to provide a belt splice whichis inexpensive, of the same thickness as the belt proper, and ofsufficient strength and flexibility to function for all the purposes forwhich the belt' is intended. These requirements are more difllcult ofattainment because modern industrial uses demand larger belts thanheretofore; many belts from 28" to wide, and from 6 to'22 feet long aresupplied. These large belts are used extensively in the polishing andsurfacing of stainless steel. There are, nevertheless, important usesfor smaller sized belts-approximately 4" wide-as in wet sandingautomobile bodies and fenders wherein there must be a perfect splice inorder not to streak or otherwise mar the work.

The present invention .provides a superior splice for joining-the endsof flexible coated abrasive strips toiform abrasive belts and disclosesin adequate detail methods of manufacture enabling those skilled in theart to practice the invention.

Referring to the drawing:

Fig. 1 shows an enlarged longitudinal crosssection of a strip ofabrasive coated web with the abrasive removed for a, small distance backfrom the end; directly over this abrasive-bared portion is a crosssectional view of an abrasive wheel used for skiving off the abrasive.

Fig. 2 is a fragmentary diagrammatic plan view of an end portion of acoated abrasive strip in position for beveling the abrasive-cleared endarea, and the abrasive wheel to be used for beveling.

Fig. 3 is longitudinal, similarly enlarged crosssection of the abrasivestrip shown in Fig. 1 after having been beveled by an abrasive wheel afragmentary cross-section of which is shown above the beveled end of thestrip.

Fig. 4 is a longitudinal enlarged cross-section of the beveled end ofthe opposite end of the abrasive-coated strip shown in Figs. 1 and 3;theabrasive wheel for beveling is shown in fragmentary cross-sectiondirectly below the beveled. end of the strip.

Fig. 5 is a longitudinal, enlarged cross-section of the mating beveledends of a belt, with adhesive coating, but prior to final splicing. I

Fig. 6 is a longitudinal, enlarged cross-section of a completed splice.

Fig. '1 is a top plan view of the completed splice shown in Fig. 6.

Fig. 8 is a vertical section of belt in position on a curvedsplice-drying support.

As an illustrative embodiment of this invention, the preparation of aspliced abrasive belt in accordance therewith and the necessarymaterials, adjustments, process steps, etc., are described below.

The coated abrasive web material is prepared by any desired process. Themore common form would be that of adhesively securing abrasive granulessuch as flint, garnet, silicon carbide, fused alumina or other naturalor manufactured abrasive to one surface of a sheet of strong rope ormanila paper althoughother felted fabrics or woven cloth can be used. Inthe majority of cases the fibrous web contains a sizing material foradditionally bonding the fibres or for imparting either firmness orflexibility, or for waterproofing purposes. The adhesive bonding agentmay be glue, silicate, synthetic resin, varnish, lacquer, etc., thechoice depending upon such factors as intended use, cheapness, strength,flexibility, resistance to cooling liquids and so direction.

abrasive web material described above. diiferent figures, like numeralsrefer .to and on.. The coated abrasive material is dried to set theadhesive bond and in many cases heat and forced air circulation are usedto facilitate the process. 'With a glue bond it is usually con- 7 cededthat a superior cutting product is obtained after the freshly driedmaterial has aged for a number of weeks, and that certain processingsteps such as splicing are scarcelyfeasible to attempt with non-agedmaterial. This invention, however, makes it possible to splice quitefreshly made coated abrasive, at least as early as ten days after itsmanufacture.

The coated abrasive material is slit into appropriate widths and thencut .to length. This cut is usually made at an acute angle .to thelengthwise direction of the strip as shown in Figs. 2 and '7, but thisis not a limiting condition as the out could be made'normal .to thelengthwise Reference is made to the drawing for a better understandingof the method of preparing and forming the splice or joint by whichendless abrasive belts are formed from the strips of coated In the thestrip passed beneath the wheel. The skived or abrasive-cleared area 3 isconveniently made about one-half an inch-wide for an average belt. A 40grit vitrified bonded fused alumina wheel of a medium hardness grade iswell adapted to perform this operation. The grinding face 6 of theabrasive wheel is dressed parallel to the axis of rotation.

Figure 2 presents a plan view of the method of carrying out the bevelingoperation and Figure 3 shows aside view of the beveling operation withthe beveling wheel slightly raised from its position in grinding, andfurther shows a crosssection of the finished, beveled area, which has-'been slightly enlarged to more clearly show the slope of the newlybeveled surface I. This illustrates the effect of traversing the skivedarea 3 of Figure 1 with a bevel-faced abrasive wheel 8. Assume forillustration that supporting web I is 0.010" thick and the distance ABis approximately one-half inch. Since there is a finite yet 1 very smallthickness of web at the end B after the beveling operation thisthickness has been taken as 0.001"; micrometer measurements indicatethisto be reasonably'accurate. The thickness -of the web at A afterbev'eling is about 0.009", hence the included angle in this specificinstance is 0 55'. Entirely contrary .to the normal expectation it hasbeen discovered that the wheel edge 9 of the abrasive wheel 8 in Figs. 2and 3 must be dressed to an angle of bevel slightly greater than, thedesired angle C to be produced on the surface-3 of the abrasive coatedstrip. For example, the abrasive wheel 8 has had its grinding edge 9dressed to make an angle 1 23' out of parallel with the axis of wheeltotation. It has been found that a single passage and return of such awheel edge will produce the desired angle C of the bevel. A wheel whichhas been found to perform this operation-successfully on supporting websfor coated abrasives is made of sharply angular white fused aluminagrit, compacted to a very open porous structure, and vitrified bondedwith a very low percentage of bond to yield an exceedingLv soft gradehardness. The wheel is rotatedat about 5000 surface feet per minute andtraversed across the work surface at a rate of 3 inches per second. Thisrate can be modified within reasonable limits, for example, as slow'asone and one-half inches per second, or as fast as four and onehalfinches per second. Any considerable departure from these limits causesglazing and burning,if too slow, or tearing, if too fast.

The opposit end of the abrasive strip 4 is now beveled as illustrated inFig. 4 to form the same angle C as shown in Fig. 3. In this operation ithas been found essential to perform the abrading with the same wheeledge angle as used to provide the beveled surface I of Figure 3; inpractice it is customary to use the identical wheel for the process.

While Figures 1 to 4 have shown the preferred method of preparing theend portions for splicing it is not desired to limit the invention tothe precise operations so depicted in detail. For example, withoutdeparting from the scope of the invention the skiving operation ofFigure 1 may be combined with the beveling operation of Figures 2 and 3.Also, instead of using an abrasive wheel such as that shown in Figures 2and 3 having a beveled grinding edge 8 it is permissible to support theabrasive strip 4 upon a table H or other suitable support which byadjustable means may be inclined slightly so as to present the narrowabrasive-cleared area to the grinding wheel at an inclination sufficientto give a satisfactory bevel, in which case a standard abrasive wheelsuch as shown in Figure 1 can be used. Alternatively the abrasive wheelitself can be tilted to give a beveling action. when the skiving andbeveling actions are combined it is found that the angle of inclinationof the grinding edge of the wheel, although always greater than theangle of inclination of the bevel, will vary depending upon the gritsize of the abrasive grain to be removed from the area 3. Generally, thelarger the grit size, the greater the angle of inclination of thegrinding edge.

Fig. 5 shows the two ends of .the abrasive strip 4 which have beenbeveled as described above; one of the ends carries an adhesive layer I!which may be any suitable material, glue, synthetic resin, rubbercompound, etc, that can be set by pressure with or without heat. Oneexample of a strong flexible cement which makes a satisfactory splice isthat sold as Graton and Knight Cement dissolved in water to a solutiondensity of 16 Twaddell at -'150 F.

The lap ends as shown in Figure 5 are placed one directly over the otherin a press with appropriately shaped presser feet and a pressureexample, one method is to suspend the belt as shown in Fig. 8 with thesplice l4 uppermost over asoasos ii. The curvature of the support inconjunction with the weight of the belt causes the inner portion of thesplice to be under a slight compressive tress while the outer portion isunder a slight tensile stress. The foregoing procedure is convenientlyapplicable to belts to feet long. Longer belts are similarly placed overcurved supports with the splices placed upon the top of the support andthe remainder of the belt coiled or resting without strain upon thejoint.

While the type of beveled splice or joint herein disclosed isparticularly applicable to abrasive coated'belts in which the backing iscomposed of paper or similar fibrous material it can also be applied tothe making of belts in which the backing is composed of one or morelayers of fabric such as cloth and the like either alone or combinedwith paper, fibre layers and so on. However, when the backing contains acloth layer or other laminated materials and it is desired to prepare asplice in accordance with the practice.

of the present invention satisfactory results can be obtained by anembrittling treatment of the splicing portions of the strip, such asimpregnation with a resinous material, as for example, aphenol-formaldehyde resin of'brittle character.

Belts incorporating the present splice are found to run more smoothlyand efficiently than the older type overlapping splice, and to beconsiderably less expensive and easier to fabricate than the butt-jointsplice used with a liner. The unexpected superiority in strength of thepresent splice in spite of its simplicity is undoubtedly due to nosingle factor in its fabrication but to the proper development andcombination of steps taken in its manufacture. For example, care inselection of the proper abrasive wheel for skiving and beveling wherebya clean, even removal is obtained without damaging or weakening theremaining fibrous structure is essential for a strong joint. "Similarlythe suspension of the newlyformed Joint over a curved support tends toprovide a splice free of wrinkles and inclined to be of uniformly strongcross-section. Likewise. other advantages and improvements accrue fromthe procedure of making belt joints such as herein described. I 7

Having set forth the invention in full detail, it is desired to claim:

1. The method of making endless abrasive belts from strips of abrasivecoated web material which comprises cutting a strip of the abrasive webmaterial of the desired width and length with the ends of the stripobliquely disposed with respect to the sides-of the strip, skiving theabrasive from a narrow area along one end of the abrasive strip,impregnating the skived area with an embrittling agent, beveling thesurface of said abrasive cleared, embrittled area, similarly bevelingthe under surface of a similar area disposed at the opposite end of saidabrasive web, applying a suitable adhesive to the beveled surfaces,bringing the beveled surfaces together in superposed relation and,applying pressure to complete the p ice.

2. The method of making endless abrasive belts from strips of abrasivecoated web material which comprises cutting a strip of the abrasive webmaterial of the desired width and length with the ends of the stripobliquely disposed with respect to the sides of the strip, skiving theabrasive from a narrow area along one end of the abrasive strip,

beveling the surface of said abrasive-cleared area, similarly bevelingthe under surface of a similar area disposed at the opposite end of saidabrasive web, applying a suitable adhesive to the beveled surfaces,bringing the beveled surfaces together in superposed relation, applyingpressure to complete the splice and suspending said newlyformed spliceupon a curved support whereby the Y coated .web material comprised ofa'fibrous backi newly-formed splice and the adhesive therein is allowedto set while the joined portions are in curved conformation.

3. The endless abrasive belt of flexible, abrasive ing and abrasivegrains adhesively secured thereto, and having a joint formed by twosuperposed, cemented end portions of gradually decreasing thicknesses,the fibers of .said backing being impregnated with an embrittling agentin the vicinity of said joint to render the backing tear-resistant, saidjoint traversing the belt in a. diagonal direction.

4. An endless abrasive beltof flexible, abrasive coated web materialcomprised of a fabric backing and abrasive grains adhesively securedthereto, and having a joint formed by two superposed, cemented endportions of gradually decreasing thicknesses, the fabric backing beingimpregnated with an embrittling agent in the vicinity of said joint torender the backing tear-resistant,

said joint traversing the belt in a diagonal direction.

5. An endless abrasive belt comprised of a layer of abrasive grainsadhesively secured to a laminated backing material one of thelaminations of which is a fabric material, said abrasive belt having ajoint formed by two superposed, cemented end portions of graduallydecreasing thicknesses, thefabrlc layer of said backing beingimpregnated with an embrittling agent in the vicinity of said joint,said joint traversing the belt in a diagonal direction.

6. In the manufacture of endless abrasive belts from strips of abrasivecoated web material the steps which comprise cutting a strip of theabrasive web material of the desired width and length with the ends ofthe strip obliquely disposed with respect to the sides of the strip,impregnating the ends of the strip with an embrittling agent, skivingthe abrasive from a narrow area along one end of the abrasive strip,beveling the surface of said abrasive-cleared embrittled area, similarlybeveling the under surface of a similar area disposed at the oppositeend of said abrasive web, applying a suitable adhesive to the beveledsurfaces, bringing the beveled surfaces together in superposed relationand .applying pressure to complete the splice,

ERIC P. min-smear. I EDGAR mm.

